1. Field of the Invention
The present invention pertains to pole structures of the type used for supporting power transmission lines, telephone wires, lighting systems and the like.
2. Description of the Prior Art
The use of wood poles in the communications and utilities industries is well-known. One advantage of wood poles over poles fabricated from other materials such as metal is their versatility. Customized on site installation of crossarms or cross bracing is accomplished in a relatively simple fashion by either drilling the poles to receive mounting hardware by use of steel mounting bands. Another important advantage is that wood poles are generally less expensive than steel poles. However, the availability of poles such as cedar in certain height categories, e.g., 70 to 100 feet, is rapidly disappearing. Accordingly, the price of wood poles beyond certain heights increases substantially and may, for certain heights, be at least as expensive as steel fabricated poles.
It is therefore desirable to provide a pole construction which can be provided at prices less than that of currently available wood poles.
A "replacement pole" arrangement is presently commercially available for replacing poles damaged by ground decay and car pole accidents and for elevation of lines and equipment on installed poles. In this arrangement, the lower, damaged section of the wooden pole is replaced while the upper section of the distributing pole including all power and telephone lines and equipment remains intact. A tapered prestressed concrete modular pole section is installed in the ground. The wooden pole is transferred onto the modular pole and is secured thereto by means of a galvanized steel connector sleeve filled with a grout.
These "replacement pole" arrangements do not appear to be particularly well adapted for providing initially installed pole structures of substantial heights. Further, concrete structures of significant length have the marked disadvantages of high weight and susceptibility to pre-installation damage.
Various techniques are known in the prior art for providing sectional poles. One such sectional pole is that of U.S. Pat. No. 3,713,262. The structure of that patent is composed of a plurality of tubular tapered sections that are locked one to each other in telescoping fashion. However, that structure is directed to metallic pole construction and is not particularly adaptable to wood pole structures.
French Pat. No. 76,767 is directed to a sectional pole and describes other structures made up of a number of tubular pieces with the lowest piece composed of either cast iron or reinforced concrete. The structure of the French Pat. No. 76,767 is a pole of two piece construction. The pole section set into the ground is cylindrical steel tube. A light metal, e.g., aluminum, section is nested on the lower section. Additional light metal sections may be added. Each section is of trapezoidal-shaped longitudinal cross-section, and as in U.S. Pat. No. 3,713,262, is adapted to nest over the lower section.
U.S. Pat. Nos. 3,217,459 and 3,839,835 teach tubular pole constructions wherein the cross-section of the pole is in the shape of a polygon. These poles are, however, of steel construction.